Download Magnets Hold a refrigerator magnet close to your refrigerator door

Magnets
Hold a refrigerator magnet close to your
refrigerator door. Let go of it. If you are close
enough to the refrigerator, the magnet will
jump across empty space and stick to the
refrigerator. This action might seem kind of
mysterious. But it makes sense when you know
what magnetism is.
Magnetism is an invisible force. Magnetic force
can attract (pull toward) or repel (push away).
Magnetism comes from magnets. Magnets
make things move without touching them.
Some magnets are weak. Other magnets are
much stronger.
Some rocks, such as lodestone, are natural
magnets. Iron and some other metals can be
made into magnets. Cloth, rubber, plastic, and
many other things cannot be made into
magnets.
SHAPES OF MAGNETS
Some magnets are shaped like the letter U. Some
magnets are shaped like bars. Magnets can also be
thin disks, squares, or rectangles. Other magnets
are round or have irregular shapes.
Magnets can be big or small. Earth is a giant
magnet. The Sun, stars, and some other planets are
also magnets. Atoms can be magnets. Atoms are
tiny bits of matter much too small to see.
NORTH AND SOUTH POLES
The important thing to remember about a magnet is
that it has two ends called poles. One end is called
the north pole, and the other end is the south pole.
The south pole of one magnet will attract and stick
to the north pole of another magnet. The south pole
of a magnet will repel, or push away, the south pole
of another magnet. North poles will also repel each
other.
MAGNETIC FIELDS
Hold the north pole of one magnet close to the
south pole of another magnet. Don’t let them touch.
You can feel the magnets tugging toward each other.
Now try to bring the north poles of both magnets
together. You can feel the magnets pushing away
from each other.
Magnets are surrounded by magnetic fields. You
feel magnetic pull or push inside the magnetic field.
Move the magnets farther apart. The pull feels
weaker. The farther you go from a magnet, the
weaker its magnetic force becomes. Magnetic fields
are strong close to a magnet and weak far away. If
you hold the magnets far enough from each other,
you will not feel them pull at all.
MAKING A MAGNET
Long ago, people in Greece, Rome, and China found
that lodestone could pull iron toward it. Lodestone is
made of the mineral magnetite. When they rubbed a
piece of iron with lodestone, the iron became a
magnet, too. People in ancient times did not know it,
but rubbing made tiny magnets inside the iron all
line up in the same direction. All the north poles
were pointed the same way. So were the south
poles.
In the 1200s, sailors learned how to make a
compass that could help them find their way at sea.
They made a needle from a thin piece of lodestone
or iron. They hung the needle from a string. The
needle always pointed north. Because Earth is a big
magnet, the south pole of the compass needle
always points toward the magnetic North Pole of
Earth. Remember, the south pole of one magnet
always pulls toward the north pole of another
magnet. This works whether the magnet is as small
as a needle or as big as a planet.
In the 1800s, people learned that magnetism is
related to electricity. They learned how to make
magnets by winding electric wire around a piece of
iron. These magnets are called electromagnets.
PERMANENT AND TEMPORARY MAGNETS
Permanent magnets always have magnetic force.
Lodestone is a natural permanent magnet. Other
permanent magnets can be made from mixtures of
metals such as iron and nickel.
Temporary magnets are made from materials that
must be inside a magnetic field to have magnetism.
Electromagnets are temporary magnets because
they must have electricity to work. Electromagnets
cannot pick up heavy loads if the electricity is turned
off.
Some materials can never be turned into magnets.
These materials include cotton, glass, paper, plastic,
rubber, and wood.
HOW WE USE MAGNETS
You can use a magnet for holding notes and
pictures on your refrigerator door. But people use
magnets for many other things. Radios and TVs
need magnets in order to work.
Electric motors need electromagnets. Electric
motors drive many appliances in your home. There
are electric motors in washing machines, vacuum
cleaners, fans, and many other things. Electric
motors also drive big machines in factories. They
drive engines in some trains and ships. Big magnets
in electric generators help make the electricity you
use in your home.
Huge electromagnets can pick up heavy loads.
Some electromagnets can even lift cars.
Electromagnets also make a powerful type of
microscope, called an electron microscope, work.
Magnetic materials can store information.
Videotapes and computer hard drives use tiny
magnets to record information.
Doctors use machines with powerful magnets to
make pictures of the inside of the body. These
pictures are made by a method called magnetic
resonance imagining (MRI).
Scientists and engineers are working on trains that
float above the track. Magnets in the train and track
push away from each other to lift the train a short
distance above the track. These floating trains are
called magnetic levitation, or maglev, trains.
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